1. Field of the Invention
The present invention relates to a chip for a force sensor that detects an external force through resistive elements and a chip for an acceleration sensor that detects an acceleration through resistive elements.
2. Description of the Related Art
In the field of automatic operating machines, such as machine tools and robots, a force is applied to a work target or an external force is received through a work operation. In this case, it is necessary for an automatic operating machine to detect external force and moment, and to perform a control in accordance with the detected force and moment. In order to perform such a control highly precisely in accordance with detected force and moment, it is necessary to precisely detect a force from the exterior (an external force) and a moment.
Hence, various kinds of force sensors are proposed so far. Conventionally known force sensors employ a fundamental configuration in which a plurality of strain detecting resistive elements are provided at deformation portions of an elastic body which elastically deforms in accordance with an external force. When an external force is applied to the elastic body of a force sensor, the plurality of strain detecting resistive elements output electrical signals in accordance with the level of deformation (a stress) of the elastic body. Based on such electrical signals, forces, etc., of equal to or greater than two components applied to the elastic body can be detected.
An example of such a force sensor is a hexaxial force sensor. Such a hexaxial force sensor divides an applied force into stress components (forces: Fx, Fy, and Fz) in individual axial directions of three axes (X axis, Y axis, and Z axis) of a Cartesian coordinate system and torque components (moments: Mx, My, and Mz) in individual axial directions, and detects those as hexaxial components.
Such a force sensor utilizes a characteristic such that the strain detecting resistive element deforms upon application of an external force and the resistance value of such element changes, detects a change in the output voltage based on a change in the resistance value of the strain detecting resistive element, thereby measuring the magnitude of an external force. The strain detecting resistive element used in the force sensor has a temperature dependency which changes the resistance value depending on a temperature. Accordingly, the resistance value varies (drifting) until the temperature of the strain detecting resistive element becomes steady after a driving voltage is applied, and the output voltage becomes also unstable originating from such a varying. Such a condition is referred to as a transient condition, and according to the conventional force sensors, it is difficult to precisely measure an external force in the transient condition.
In order to reduce a time (a transient condition) until becoming a steady state after a voltage is applied, a semiconductor pressure sensor disclosed in JP2009-175088A employs a configuration in which a semiconductor substrate is provided with a heater electrode, a strain detecting resistive element (a piezo resistor) is heated through the semiconductor substrate by the heater electrode in order to promote heat generation, thereby shortening the time of a transient condition.
The semiconductor pressure sensor of JP2009-175088A has, however, a restriction such that individual functional elements must be laid out within a limited space. Accordingly, although the heater electrode is formed at a circumferential edge of the semiconductor substrate which is apart from the strain detecting resistive element, there is a time lag until heat is transmitted to the strain detecting resistive element located in the vicinity of the center through the semiconductor substrate, and there is varying in temperature among respective resistive elements. In order to eliminate such time lag and temperature varying, when the voltage applied to the semiconductor substrate is increased, the production cost increases and the semiconductor substrate may be deformed due to heat.